Geomorphic Response of Glacial Decoupling in Alpine Regions in Response to Climate Warming: Icy Debris Fans and Early Paraglacial Landscape Evolution

近几十年来，气候变暖对高山冰川区的影响尤为显著。许多山谷冰川已经与高层冰盖分离，暴露出主要的悬崖，目前正在经历由冰主导的过程，包括冰雪崩、岩崩、冰碎屑流和泥流雪崩，导致的快速质量消耗。该项目将首次详细研究在这些悬崖底部进化的一套动态冰主导地貌（这里称为冰碎片扇）。先前对冰川消融景观的研究，在所谓的副冰川时期形成，描述了冲积扇和talus锥的快速发展，然而，冰主导的大块浪费过程对地貌演化的影响大多未被认识到。研究将在阿拉斯加和新西兰的研究地点进行，这些研究地点提供了最多样化的形态发生环境和时间阶段，需要为与冰碎片扇相关的地貌建立一个准确的进化模型。本研究将侧重于野外调查，旨在破译形成冰碎屑扇的沉积过程，流域形态对扇形态的影响，并将冰扇的沉积学特征与非冰为主的类似地貌进行比较。通过使用基于地面的激光雷达测绘调查、延时摄影和遥控飞机的新颖组合，我们将量化在不同环境下形成的沉积过程的速率和体积以及扇的形态随时间的变化。地表沉积学数据和地下地球物理调查将记录冰碎屑扇的沉积结构。一旦整合，这些数据集将对冰碎屑扇的形成和演化产生重要的约束，并对评估景观随时间的演化具有重要意义，包括将冰碎屑扇的沉积与相关但更深入研究的地貌（如冲积扇和距骨锥）区分开来。最近的气候变暖对冰川产生了重大影响，冰川从高海拔冰盖向低海拔山谷冰川输送冰。气候变暖导致许多山谷冰川与其源冰盖分离，从而暴露出主要的基岩峭壁。这些悬崖非常不稳定，以冰为主的极端侵蚀过程为特征。比如冰崩、冰泥石流、泥崩和岩崩。快速形成的地貌被称为冰屑扇，在冰川消退后迅速形成的新景观中占据主导地位，在夏季的几周内，数百次灾难性的冰崩和冰屑流是常见的。这项研究直接解决了与现代全球变暖相关的几个关键科学问题，并将通过开发一种涉及延时摄影、地面雷达成像和遥控飞机的新方法，推进崎岖高山环境中地形分析的研究方法。考虑到冰屑扇是新发现的地貌，我们的研究有望为冰川消融的高山环境中地貌演化的本质提供新的视角。预期的结果将对改善冰川消融的高山环境中地质灾害的评估和流域管理产生直接影响。具体来说，结果将更好地了解下游沉积物和水通量的变化，提高我们对阿拉斯加和新西兰国家公园偏远地区的危害和安全的理解。随着冰川在高山环境中不断融化和变薄，预计各种冰川灾害将会增加，包括落石、冰坝爆发的洪水和冰崩。随着斜坡变得越来越不稳定，冰碎片扇将变得更加普遍。更好地描述这些鲜为人知的过程和地形的性质和频率，将有助于减轻这些影响越来越大的地理区域的危险现象的影响。该项目得到了地貌与土地利用动力学项目、美国国家科学基金会国际科学与工程办公室以及EAR教育与人力资源项目的支持。

In recent decades, the impacts of climate warming have been especially significant in alpine glaciated regions. Many valley glaciers have decoupled from high-level icecaps to expose major escarpments now experiencing rapid mass wasting by processes dominated by ice, including ice avalanching, rockfalls, icy debris flows, and slush avalanches. This project will conduct the first detailed study of a suite of dynamic ice-dominated landforms (here termed icy debris fans) that are evolving at the base of these escarpments. Previous studies of deglaciating landscapes, formed during periods known as paraglacial, have described rapid development of alluvial fans and talus cones, however, the influence of ice-dominated mass wasting processes on landform evolution has mostly gone unrecognized. Research will occur at study sites in Alaska and New Zealand that provide maximum variety of morphogenetic settings and temporal stages needed to develop an accurate evolutionary model for landforms associated with icy debris fans. This research will focus on field investigations aimed at deciphering the depositional processes that form icy debris fans, the influence of catchment morphometry on fan morphology, and distinguishing sedimentological characteristics of icy fans compared with similar landforms not dominated by ice. By using a novel combination of ground-based LiDAR mapping surveys, time-lapse photography, and remote-control aircraft, we will quantify variations in the rates and volumes of depositional processes and morphology of fans formed in different settings through time. Surficial sedimentological data and subsurface geophysical surveys will document the sedimentary architecture of icy debris fans. Once integrated, these datasets will yield important constraints on the formation and evolution of icy debris fans and hold implications for evaluating landscape evolution through time, including distinguishing the deposits of icy debris fans from related but more thoroughly studied landforms such as alluvial fans and talus cones. Recent climate warming has had major impacts on glaciers delivering ice from high-level icecaps to lower elevation valley glaciers. Warming has resulted in decoupling of many valley glaciers from their source icecaps, thereby exposing major bedrock escarpments. These escarpments are highly unstable and characterized by extreme erosional processes dominated by ice ? such as ice avalanches, icy debris flows, slush avalanches, and rockfall. Rapidly-forming landforms known as icy debris fans dominate this newly-forming landscape immediately following deglaciation where hundreds of catastrophic ice avalanches and icy debris flows are common during summer weeks. This research directly addresses several key scientific problems linked to modern global warming and will advance research methods of landform analysis in rugged alpine environments by developing a novel methodology involving time-lapse photography, ground-based radar imaging, and remote-controlled aircraft. Given that icy debris fans are newly discovered landforms, our research holds promise for providing new perspectives on the nature of landform evolution in deglaciating alpine environments. The anticipated outcomes will have direct implications towards improving assessment of geohazards and watershed management in deglaciating alpine settings. Specifically, results will provide a better understanding of changes in sediment and water flux downstream, improving our understanding of hazards and safety in back country areas of national parks in Alaska and New Zealand. As glaciers continue to melt and thin in alpine environments, a wide range of glacial hazards are expected to increase, including rockfalls, breakout floods from ice dams, and ice avalanches. Icy debris fans will become more prevalent as slopes become increasingly unstable. Better characterization of the nature and frequency of these poorly understood processes and landforms will help mitigate the impacts of these hazardous phenomena that are affecting increasingly larger geographic regions.This project is supported by the Geomorphology and Land Use Dynamics Program, NSF's Office of International Science and Engineering, and EAR's Education and Human Resources program.